The parasite's real interests, however, are cats and rodents.
T. gondii can live in any warm-blooded creature, but it
prefers to end up in the gut of a cat, where it can breed.

To do so, the parasite takes control of the minds of its rodent
hosts, making the
smell of cat urine sexually appealing to them rather than
scary. That ups the chances a rodent will cozy up to a cat and
get scarfed down, along with the parasite.

How T. gondii gets in

T. gondii spreads into humans through contact with
infected animal feces or undercooked meat. Questions remain about
how the parasite is so successful at evading the immune system
and infecting the body, however. Swedish researchers led by
Antonio Barragan of Karolinska University Hospital Huddinge in
Sweden wanted to find out.

Earlier studies had found that an infection by T. gondii
makes a certain type of immune cell go haywire. These cells,
called dendritic cells, are spiny little free-floaters that move
throughout the body's tissues.

When a dendritic cell meets a foreign invader, it engulfs and
processes it, carrying the pieces to lymph nodes, which then
launch a full immune attack.

When infected by T. gondii, dendritic cells start moving
at hyper-speed. Barragan and his colleagues suspected that the
parasite might be invading the cells and using them to get around
the body like a city bus, but they didn't know how. [Top
10 Most Disgusting & Diabolical Parasites]

Chemical hijacking

By infecting both human and mice dendritic cells with the
parasite, the researchers found the cells suddenly produced
increased levels of GABA, a neurotransmitter that is important
for brain cell function.

GABA also makes dendritic cells go, the researchers found —
infected cells making more of the chemical began moving in more
random directions and did so faster than uninfected dendritic
cells.

"For toxoplasma to make cells in the immune defense secrete GABA
was as surprising as it was unexpected, and is very clever of the
parasite," Barragan said in a statement.

The researchers then infected live mice with T. gondii
and treated some of them with compounds that inhibit the release
of GABA. They found that in treated mice, parasite levels were
2.8 times lower than untreated mice four days post-infection.
Those findings suggest that T. gondii is indeed
using the immune system as a free ride around the body.

The findings are published today (Dec. 6) in the open-access
journal PLOS
Pathogens.